This invention generally relates to systems used to detect failure of gas turbine engines and more specifically to a gas turbine engine shaft failure event. The new detection system uses the physical breaking of an electrical circuit that includes redundant wiring and associated electronics to detect a turbine engine broken shaft.
Gas turbine engines generally include rotating shafts having compressor rotors driven by turbine rotors and other elements attached thereto. The engine shaft in operation rotates at high speed in a turbine having limited tolerance for longitudinal motion of the shaft and its components. If there is an engine failure which allows axial longitudinal motion of the shaft relative to other engine elements the detection of such motion may be used to activate the shut off of the engine thereby minimizing further damage to the engine and preventing turbine overspeed which, for a gas turbine engine such as on an aircraft, may be catastrophic. The shaft breakage may result from bearing failure, imbalance, or other reasons.
Traditionally the failure detection system for gas turbine engine shafts has involved complicated mechanical linkage and hydraulic elements to detect engine failure and cause the shut off of the engine. An example of a single thread electro-optic sensor system is disclosed in U.S. Pat. No. 5,411,364. This sensor system eliminates the need for complicated mechanical mechanisms by use of a single optical communication link that is routed through the stream of gas flow in a sensor element slightly downstream of a rotor element. If a failure or other event causes axial motion of the turbine rotor in the direction of the optical communication link such that a rotor element impacts the sensor, the optical communication link is broken which condition may be detected as the absence of an optical signal. This system requires use of active electro-optical components, such as, light emitting diodes and light activated diodes, near the turbine or use of optical wave-guides and other components for sensing and transmitting. Use of such components in or near the turbine is undesirable as the turbo machinery represents an inhospitable environment for such equipment that may result in sensor failure and false indication of engine failure.
The use of electromechanical switches to detect compressor failure has been disclosed in U.S. Pat. No. 3,612,710. While this invention discloses a primarily mechanical switch with electrical continuity/discontinuity features, it is complex in operation, which may lead to failure of the sensor and false indication of compressor condition. There is no provision to distinguish an open circuit due to the rotor or impeller movement from a failure of the electrical circuit elements. While such lack of differentiation may not be critical for the disclosed compressor application, a false indication for a gas turbine engine such as on an aircraft may be catastrophic.
As can be seen, there is a need for a reliable detection system with a low probability of false indications that is based on a simple mechanism to sense axial motion of a turbine engine rotor shaft.
An improved gas turbine engine broken shaft detection system according to the present invention comprises a redundant electrical circuit closed by a breakable wire link in communication with detection and control elements for shut off of a gas turbine engine in the event of rotor shaft failure as for example a broken shaft.
In one aspect of the present invention a broken shaft detection system for detecting a gas turbine engine broken shaft comprises a detector assembly having a plunger assembly for axial displacement against a link that forms continuity in a circuit detection element. When the link is broken by axial displacement of the plunger the open circuit created may be detected by a detection and test element that communicates such open circuit to an overspeed circuit. The overspeed circuit controls a shut off switch to actuate a shut off valve to halt fuel flow to the engine. The circuit detection element has two pairs of parallel wires for connection between the link and the detection and test element that enables the system to differentiate between a broken link and a broken wire or wires elsewhere in the interconnections and provides for redundancy and testing of the health of the system.
In another aspect of the invention a method for detection of a broken shaft in a gas turbine engine comprises mounting a detector assembly downstream of a power turbine wheel; positioning a plunger of the detector assembly to be displaced against a link in the event of rearward motion of the power turbine wheel; sensing the breaking of the link; and communicating the breaking to a shut off valve to stop fuel flow to the engine. The detector assembly link may be connected to a detection and test element by two pairs of parallel wires for redundancy and to facilitate testing by measurement of current for open circuit detection; monitoring for current ground paths parallel to the link; and self testing of wires to check open circuits not attributable to the link breaking.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.